The overall objective of this research is to determine the role of structure of biomolecular systems in determining their dynamic electronic properties. Toward this end, modern methods of field theory and many-body theory are being used to formulate optical properties and related electronic interaction effects in helical polymers, especially polynucleotides. Three specific areas are as follows: (1) The nucleic acid bases are being studied in terms of linear response theory, in which the Time Dependent Hartree (TDH) level of approximation is used to obtain the density response function for pi-electrons. This enables the calculation of absorption spectra (including polarizations) and atom-centered transition densities. (2) The linear response tensor in the TDH approximation is developed for helical polymers in a manner which fully utilizes symmetry and exciton selection rules in order to provide simple, closed-form expressions for circular dichroism spectra. The theory naturally emphasizes the role of molecular geometry. (3) The effects of bandwidth and degree of stationarity on coherent, nonlinear response properties of molecules are being studied, with particular emphasis on developing models for infrared laser photochemistry.